Legumes Should Be Supplemented with Nitrogen for Optimum Results



One of the bird of the desert bird of paradise, a legume.
Most legumes have characteristic flowers and leaves.

Q. Do nitrogen fixers like trumpet vines and locust trees provide significant nitrogen to nearby plants?  For example the Bermuda lawn surrounding the locust or the iris and daffodils in a flower bed anchored by a trumpet vine.

 

A. No they don’t produce enough for our high expectations in landscapes and gardens. Nitrogen fixers (such as legumes, there are others) supply enough to help make sure they can reproduce and make seed. The objectives (if I can put it in human terms) of plants and humans are different. Plants want to survive, reproduce and out-compete with other plants for their niche. In nitrogen poor soils nitrogen fixers, like legumes, take nitrogen from the air and supplement what they can’t get from the ground. In nitrogen poor soils, legumes are fantastic competitors. In nitrogen rich soils they are not.

Typical legume flower leaf and pod

            The expectations of humans for the plants they care for are far greater than plant objectives. We want beauty and lushness from landscape plants and we want a good production of food from our legume crops.

            The nitrogen needed to meet human expectations is far greater than the nitrogen needed to meet plant objectives. So for this reason, we need to fertilize nitrogen fixing plants with nitrogen to meet our objectives. The basic rule of thumb I use is the question, “So I want my plants to meet what they consider to be adequate (reproduction and beat out the competition) or do I want them to do more than that?”

Snow pea flowers and leaves are good examples of what
many legumes resemble

            Most people want these plants to do far more than successfully reproduce. Some people are purists and they want that “native look” or for philosophical reasons they prefer the plant produce what it can they are happy living in the "nitrogen cycle".  Nothing wrong with that and it meets their expectations. If you want lushness or greater production, then add extra nitrogen.

            The general rule of thumb you can follow is that many nitrogen fixing plants receive only about 25%, at best, of the nitrogen they need to meet our expectations. However you can treat legumes just like any other plant and feed them extra nitrogen. Plants can be lazy. If you give them all this nitrogen, they may produce little to no nodules on the roots (the nodules contain the nitrogen fixing bacteria). Hey, its alot easier to take available nitrogen than it is to build these homes on their roots for these symbiotic bacteria that take nitrogen from the air.

root nodules of legume can resemble root knot nematode infestation

            We are lucky in that nitrogen fixation by legumes is far more efficient in our alkaline soils of the desert than in acid soils of high rainfall areas. So to answer your question with a short winded response, no, they will not produce enough nitrogen for surrounding plants if your landscape expectations are high. If you are a eco-purist, then maybe they will.

Removing Sucker Growth from African Sumac

Q. I have an African Sumac that has sprouts coming up from the roots. Besides trimming them every time they get above the soil level is there anything I can do to stop these sprouts from popping up?

 



Suckers coming from tree rose. These should be removed from
the roots by pulling back the soil and pulling them if they are
young enough. If older they should be cut off below ground.

A. I think I have enough information to answer. If these are naturally occurring “sprouts” and not coming from a damaged area then I would say no. However, usually if you keep these suckers controlled as soon as you see them and remove them at the trunk, not cutting them off with a shears, the number should slow down considerably.

            There are chemicals you can apply that are sprout inhibitors but I don’t think you have access to those chemicals as a consumer and not a professional. Besides, even if you did have access to them they would probably be expensive for you and a real pain to apply it. The best way to reduce the numbers is make a short term commitment to remove them as soon as you see them. Remove them directly from the trunk.

            This may mean you will have to remove some soil from the trunk and cut them as close to the trunk as you can. As you see new sprouts a couple of inches long, immediately pull them from the trunk.

            If you keep this up and do not let them get large before you remove them then I think you will see a reduction in numbers and easier maintenance. I wish there was a magic bullet for you but I doubt it.

Use Plants Resistant to Nematodes

Q. You have covered on one of your post about nematodes. Last fall, I pulled one of my cucumber plants. There were 4 plants in a row. One of the plants definitely had strange roots which I am almost positive were caused by root knot nematodes. I didn't do any solarization because it was cold during the time and I have read that it is best to do it during the hottest months. Are these nematodes harmful to humans and my dog? Will it give me a disease or worm if I touched the soil?

Swelling bumps on roots is root knot nematode infestation

You have covered that the only other way to fix this completely is through fumigation--which I can't really do since I only do organic gardening. Can I at least plant any other vegetables in the same raised bed, or will it cause me any ill effects after I eat the fruit/veggies that it bears? I was also thinking of maybe removing the soil from the raised bed and move them to the big pots where I will be planting citrus plants. Then I will replace the raised bed with new soil. Would this work well or will it just cause problems to my citrus plants? I'd love your input.

 

Root know nematode on tomato

A. Nematodes are very tough to impossible to get rid of if you have them. I should say they are basically impossible to get rid of. Be careful and do not move soil from this spot to other areas or you will move the nematodes as well.

Nematodes only infest plants, not animals so all animals are safe around these guys. Soil solarization will help knock back the populations but not get rid of them.

There are some products like Clandosan (a natural product) which are supposed to help but I would not be too optimistic. Even with fumigation it does not get rid of them buy just knocks them back.

            Use vegetables that are nematode resistant and fruit trees on rootstocks that resist nematodes. On vegetables they will have the designation "N"below the name somewhere. Other letters might also appear like "V" "F" and the like which just stands for resistant to other pest problems like Verticillium (V) and Fusarium (F), two prominent disease problems.

Nematode resistant rootstocks for fruit trees include Nemaguard, Citation, Viking, Atlas, Myrobalan, and Marianna. Hope this helps.

 

Organic Control of Stinkbugs

Q. What is the best way to control Shield Bugs here in Las Vegas?   They were found on my Italian Cypress.   My concern is that they will invade my garden.  The broccoli and cabbage seem to be ok right now but the new garden is going in this week.  

Shield or stink bug. They have a hypodermic-like mouthpart
lying under their abdomen that can pierce fruit or vegetables
and withdraw fluids.

A. These can also be called “stink bugs” because it can release an odor from its abdomen when attacked or threatened. Many of these types of insects will damage fruits and vegetables and they have no really good predators here for them. Even birds will leave them alone because of their “stink”. 

            We will find lots of bugs on our plants. It is really the numbers that count. They are overwintering right now and waiting for a chance to find some food with the new growth and make some babies. I would at this point just hand pick them when you see them and put them in a bottle with vinegar or alcohol.

Stinkbug and apple to give you relative size. The dimples
on the fruit were probably caused by stinkbug feeding

            If you do not need to use a pesticide, I wouldn’t. These guys have wings under that shield and can fly from yard to yard. Pesticides used unnecessarily will also kill other insects, good and bad.

            Also if you just take a spray bottle with soap and water and spray them directly this will also kill them. This is true of all insects, good and bad. The water is made “wetter” or it loses its surface tension and can then invade the tiny spiracles that insects have on their body for taking in air and “breathing”. This causes them to basically drown.

            Soap and water sprays are good to use but must land directly on the insect to “drown” it. It will not leave a poisonous residue behind like pesticides can.